It has long been known that the conduction velocity of a nerve is affected by the health of a nerve. Disease affecting a nerve or injury to a nerve is generally accompanied by a decrease in nerve conduction velocity.
Carpel tunnel syndrome is a neuropathy of the median nerve occurring in the segment of the nerve which lies in the carpal tunnel within the underside of the wrist. This neuropathy ("sickness of the nerve") is associated with disease of or injury to the median nerve in the carpal tunnel. Carpal tunnel syndrome is becoming an increasingly significant health problem due to the changing demographics of the work population and the aggravation of this underlying biologic predisposition for the development of carpal tunnel syndrome by the stresses of the work environment. The incidence is rapidly increasing, and the costs associated with its treatment and with work-related disability are escalating. Because job-related activities are often a factor in carpal tunnel syndrome, it has become a major concern of employers, workers compensation insurers, and government agencies having jurisdiction over conditions in the workplace. At present, approximately half of all workers compensation claims are based on cumulative trauma disorders, also known as repetitive motion injuries. These injuries are predominantly carpal tunnel syndrome.
Despite the fact that carpal tunnel syndrome is a disease of insidious onset in which the nerve is progressively injured day by day, a patient typically does not seek medical attention until the condition has become sufficiently bothersome or painful as to interfere with normal activities. Unfortunately, by this time, the syndrome is often far enough advanced that surgery is the only effective treatment. Frequently after surgery, the patient cannot return to normal repetitive activities without risk of recurrence or complications.
Others have used nerve conduction velocity measurement to assist in diagnosing carpal tunnel syndrome in patients presenting with symptoms consistent with this condition. However, such prior art measurement systems suffer from a number of drawbacks rendering them unsuited to screening of an asymptomatic individual for the likelihood of developing carpal tunnel syndrome, which would permit safe and inexpensive prophylactic measures to avoid ormitigate the syndrome. Currently the measurement is performed using expensive, multi-purpose equipment, by testing personnel who are highly skilled in electrophysiology. The test may be made by applying a stimulating electrical pulse to the patient's skin, such as on the arm, and recording the distally occurring electrical signal, which has been propagated down the nerve in response to the stimulus pulse, such as at the patient's hand or fingers. The tester first attaches stimulating and pickup electrodes to the patient, generally by taping the electrodes to the patient's skin or perhaps surrounding the patient's finger(s) with nooselike wire electrodes. The electrodes are connected to a multi-purpose EMG machine, which generates electrical stimulating potentials and displays the action potential (also known as the depolarization curve) received by the pickup electrodes on a CRT or other display. The stimulating signal may be increased until an adequate number of nerve fibers are depolarized to produce a response waveform which is satisfactory in appearance to the tester. The tester then manually moves a cursor across the CRT screen to what appears to be the peak response of the action potential. The elapsed time between the stimulus and a maximal point on the response waveform is expressed in milliseconds. The tester measures the distance between the stimulus and pickup electrodes, and calculates the nerve conduction velocity by dividing the measured distance by the measured elapsed time.
The foregoing system generally allows variation of many parameters which should be controlled, and cannot be used in a cost-effective manner in the typical work environment. An on-the-job test is also subject to a range of environmental conditions which may be quite different from those in a neurologist's office, such as temperature variations which affect nerve conduction velocity and therefore interfere with interpretation of the test results.
The variable parameters in the prior art systems which ought to be controlled are generally the result of requiring a person, albeit a trained electrophysiologist, to set up and administer the test. For instance, the location and spacing of the electrodes and the visual selection of the maximal point of the response waveform on the CRT to determine the elapsed time are subject to inaccuracies, errors, and variations among testers. Moreover, the requirement of an in-office test by trained electrophysiologist using expensive, multipurpose equipment and the time-consuming nature of the prior art test render it expensive, and unlikely to be used as a screening technique due to the extensive time that the worker must be away from the workstation in order to complete the test. For these reasons, nerve conduction velocity tests have been used primarily as a means for confirming diagnosis of carpal tunnel syndrome rather than for prophylactic screening, treatment recommendation, and treatment monitoring.
Another drawback of prior art systems which have been used to monitor carpal tunnel nerve conduction velocity is the unavailability of an easily usable digital data output. For instance, certain known systems provide response waveform data as an image in a graphics file. This requires excessive data storage space, which is always undesirable but particularly so if the system is to be used to perform many tests in a remote field location. Moreover, it is difficult to extract pertinent data from a test result stored as an image, which renders comparison of results from different tests quite difficult.
It is therefore a general object of the invention to provide a neurological monitoring system which avoids the above-described drawbacks of the prior art.
It is a more specific object of the invention to provide a neurological monitoring system which is useful for prophylactic screening, treatment recommendation, and/or treatment monitoring in connection with carpal tunnel syndrome.
It is another object of the invention to provide a neurological monitoring system which does not require highly skilled personnel for effective use.
It is another object of the invention to provide a neurological monitoring system which may be easily used in a wide variety of locations, including work areas.
It is another object of the invention to provide a neurological monitoring system which reduces errors in the placement of electrodes and determination of the distance between them.
It is another object of the invention to provide a neurological monitoring system which reduces errors in the determination of elapsed time between stimulus and response.
It is another object of the invention to provide a neurological monitoring system in which response signals generated by sensory nerves may be used.
It is another object of the invention to provide a neurological monitoring system which facilitates storage of data relating to test circumstances as well as the test results.
It is another object of the invention to provide a neurological monitoring system which facilitates correlation of data from different tests.
Finally, it is an object of the invention to provide such a neurological monitoring system which is simple, rugged, reliable, and inexpensive.
In accordance with the foregoing objects, the neurological monitoring system of the present invention comprises a portable, substantially automatic nerve conduction velocity monitoring system. The monitoring system includes stimulating and pickup electrodes disposed in a fixed relationship to one another, adapted to contact skin areas on the forearm and hand, respectively, adjacent nerves passing through the carpal tunnel. The monitoring system further includes means for applying stimulus electrical signals to the stimulating electrodes, and means for processing and storing data relating to the electrical signals received at the pickup electrodes.
Other objects and features of the invention will become apparent to those skilled in the art in view of the following specification and claims and the drawings.